As the requirements for smaller and smaller bandwidths continue to advance along with the integrated circuit design and manufacturing constraints necessary to follow Moore's law, and other associated beam parameter restraints, e.g., beam energy and bandwidth stability pulse to pulse over a relatively large number of pulses, e.g., hundreds of pulses, e.g., in a burst of laser light source pulses, e.g., used in exposing photoresist on an integrated circuit wafer, e.g., over a single die or a portion of a single die on such a wafer, e.g., as used in a photolithography scanner, the need to control laser light pulse wavefront becomes more and more critical, along with the need to ensure essentially constant wavefront pulse to pulse or at least to insure the entire laser system can react to and compensate for wavefront changes in relatively real time, e.g., pulse to pulse or almost pulse to pulse, to at least compensate for wavefront change effects within a burst, between bursts in preparation for a next burst and after a longer laser downtime than from burst to burst and also due to such changes in real time such as duty cycle. It is known that these types of changes in laser operation cause a number of effects, e.g., in the line narrowing module (“LNM”) where bandwidth of the laser output is selected, and elsewhere, e.g., thermal effects, which influence wavefront and thus the operation of the LNM in selecting bandwidth, as is noted in at least one of the above referenced co-pending applications and issued patents of applicant's assignee, Cymer, Inc. It is also known to use stimulatable materials, e.g., electrically or magnetically sensitive materials, e.g., PZTs to bend and twist the grating of an LNM for the purpose of modifying the grating's shape to account for changes in wavefront. In addition, a motor driven bandwidth control device (“BCD”) is known as shown in at least one of the above referenced applications or patents assigned to applicants' assignee Cymer, Inc., wherein a threaded shaft with a cooperating spring places compressive or tensile forces on a grating held in a mounting to which the BCD is attached, with the motor rotating the shaft for active grating bending control and thus wavefront adjustment. To varying degrees, however, the possible ways to apply the desired compressive and tensile forces have certain drawbacks to being able to actively control the grating shape for wavefront control, e.g., the addition of heat, and thus thermal effects, into the LNM and surrounding laser system modules or module components that can cause undesirable short term and/or long term wavefront transients. There is a need, therefore, for an improved mechanism for both passive and active control of the BCD in the LMN.
U.S. Pat. No. 5,095,492 referenced above relates to a line narrowing module (unit) with a bendable grating and bending the grating to compensate for beam divergence caused in the laser resonance cavity. U.S. Pat. No. 5,970,082, referenced above relates to a gas discharge laser with an unstable resonance cavity having a cylindrical mirror and a bendable grating to compensate for the wavefront modification due to the cylindrical mirror. U.S. Pat. No. 6,094,448, referenced above, relates to structural details of the grating bending mechanism, which is only passively used to control grating shape, though the '492 patent was incorporated by reference which discloses active control. U.S. Pat. No. 6,192,064, referenced above, relates to an LNM with various tuning means for tuning wavelength output to less than 0.1 pm using computer control in which also has a grating curvature mechanism using a stepper motor. U.S. Pat. No. 6,212,217, referenced above, relates to a gas discharge laser with an LNP having a bendable grating under computer control based on wavemeter feedback. U.S. Pat. No. 6,493,374, referenced above, relates to a wavefront correction means controlled by a computer to bend a grating in curvatures more complex than simple concave and convex shapes. U.S. Pat. No. 6,496,528, referenced above, relates to an LNM including purging means and a grating flexural mount that may be two parts of the mounting secured to the LNM housing and only one secured to the grating substrate or the two parts secured to the grating substrate and only one secured to the LNM housing, e.g., with an H-flex joint or a dovetail sliding joint. U.S. Pat. No. 6,532,247, referenced above, relates to a gas discharge laser system with an LNM with a piezoelectric grating illumination angle controlled with feedback control, including also a pivotable grating. Ser. No. 10/808,157, referenced above, relates to nominal center wavelength and bandwidth selection optics with flexure mounting. Ser. No. 10/820,261, referenced above relates to nominal center wavelength and bandwidth selections optics for generating multiple spectra with respective nominal center wavelengths separated by a selectable differential wavelength. Ser. No. 11/000,571, referenced above relates to a grating with different bending mechanisms to bend the grating in different ways, e.g., to change the ratio of an E95% bandwidth measurement to a FWHM bandwidth measurement. Ser. No. 11/173,988, referenced above relates to methods and apparatus for controlling wavefront and thus bandwidth using, e.g., optical elements in the laser cavity. Ser. No. 11/254,282, filed on Oct. 20, 2005, referenced above relates to an active bandwidth adjustment mechanism, e.g., controlling an active bandwidth adjustment mechanism utilizing an algorithm implementing bandwidth thermal transient correction, e.g., based upon a model of the impact of laser system operation on the wavefront of the laser light pulse being generated.